29-06-2020, 07:46 PM
(This post was last modified: 29-06-2020, 07:52 PM by Mike Watterson.)
The 1j42a and 1j37a are fantastic mixers, but only using a separate oscillator and f1 as common mode to g1a and g1b and f2 as differential on g1a and g1b, otherwise poor.
Without the transformer with RF and LO on the centre tap it's best to tie g1a and g1b and use it as a mixer the same way as a 1j24b, that is a separate triodised 1j24b (or 1j42a) as an oscillator and tie the oscillator anode direct to the mixer valve's g2 as the only g2 bias. RF then to mixer g1 and IF from mixer Anode. I've tested this plugged direct into a DK96 socket, with NO additional parts, using the 1j24b, other than a small resistor in each of the f- leads to drop voltage by 0.25 volts.
Because the Rod designs are very linear, the best mixing action without the g1a and g1b special drive is signal on g1 and LO on g2. That's how mixers were done with regular valves before Hexodes or Pentagrids were invented.
A single valve as mixer oscillator will work, but rubbish compared to two valves unless it's a Heptode, Octode or Nonode.
Without the transformer with RF and LO on the centre tap it's best to tie g1a and g1b and use it as a mixer the same way as a 1j24b, that is a separate triodised 1j24b (or 1j42a) as an oscillator and tie the oscillator anode direct to the mixer valve's g2 as the only g2 bias. RF then to mixer g1 and IF from mixer Anode. I've tested this plugged direct into a DK96 socket, with NO additional parts, using the 1j24b, other than a small resistor in each of the f- leads to drop voltage by 0.25 volts.
Because the Rod designs are very linear, the best mixing action without the g1a and g1b special drive is signal on g1 and LO on g2. That's how mixers were done with regular valves before Hexodes or Pentagrids were invented.
A single valve as mixer oscillator will work, but rubbish compared to two valves unless it's a Heptode, Octode or Nonode.
